The invention relates to a signal branch for use in a communication system, in particular a reflector antenna for transmitting microwave signals. The invention further relates to a method for processing a received signal fed into a signal branch.
Due to their very narrow beam characteristic, large reflector antennas require a very precise alignment relative to a transmitter and/or receiver, generally a remote station. A beacon signal emitted by the remote station is used for the alignment. In order to analyze the beacon signal by means of the reflector antenna, an alignment diagram is required with a zero point in the primary beam direction. If the beacon signal deviates from the primary beam direction, an additional signal is received that can be used to correct the directional deviation. The transmission, separation, and analysis of the beacon signal occurs in addition to the transmission of the actual communication signal. In so doing, the beacon signal may not influence the communication signal.
A reflector antenna for the transmission of microwave signals typically comprises a signal branch that has a common signal wave guide for transferring a transmission signal and a received signal. The common signal wave guide comprises one first and one second end as well as an exterior and an interior. A horn is connected to the first end of the common signal wave guide, by way of which the transmission signal departing the common signal wave guide is decoupled and the transmission signal in the common signal wave guide is coupled. As a rule, a plurality of signal wave guides is provided along with the common signal wave guide for feeding the transmission signal and for decoupling the received signal. The signal wave guides are, for example, disposed in a symmetrically distributed fashion on the exterior of the common signal wave guide and are each connected to the common signal wave guide in a communicative manner.
In particular, the signal branch has the task of processing a mode mixture of modes of the received signal in such a way that a differentiation occurs between the original communication signal and correction data for the communication signal. At the same time, the signal branch must correctly transfer a transmission signal fed into the plurality of signal wave guides to be decoupled by the horn. The ensuing conflict of objectives between correctly distributing the received signal with regard to its communication and correctly distributing the correction information and decoupling the transmission signal with the desired polarization from the reflector antenna has not always been satisfactorily resolved up to now.
The signal branch shown on page 54 of “Corrugated Horns for Microwave Antennas” by P. J. B. Clarricoates and A. D. Oliver has the disadvantage that separation of transmission and received signals is not possible, such that the signal branch is only suitable for receiver antennas.
U.S. Pat. No. 6,714,165 B2 discloses an orthomode transducer (orthomode transducer OMT) having a circular coaxial wave guide supply system. In this arrangement, the correction information necessary for correcting the communication signal, known as tracking modes, are not propagable in the reception path, so that the correction signal cannot be acquired.
The same problem is present in the signal branch disclosed in U.S. Pat. No. 6,657,516 B1. Here, the signal branch comprises a wave guide structure having one exterior and one interior wall, which form one exterior and one interior wave guide chamber. These chambers are connected in a communicative manner with the horn on one end of the signal branch. The exterior wall comprises one cylindrical section and one conical section, with the cylindrical section and the interior wall being oriented coaxially relative to one another. Moreover, symmetrically disposed signal wave guides are formed in one reception path around the cylindrical section, which are also coupled to the exterior chamber in a communicative fashion by means of impedance adapter blinds matching irises.
The publication “An X-band single horn autotrack antenna feed system” by Yodokawa, T. and Hamada, S. in Antennas and Propagation Society International Symposium, 1981, June 1981, vol. 19, pages 86-89, discloses a multi-mode coupler. This coupler uses the modes TE11 and TM01 to effect a correction of a circularly polarized communication signal. However, the method described by this publication allows the processing of only a “tracking” mode (TM01). The term “tracking” is to be understood as the processing of correction information in order to increase the precision of the communication signal. Moreover, the polarization effects directly degrade the orientation accuracy to be attained in orienting the reflector antenna as an error. Thus, the method described is not suitable for applications requiring high degrees of accuracy.
The antenna system described in the publication “Modal analysis and design of the dual-band orthomode junction” by J. Bornemann and J. Uher, Proc. ANTEM 2002, pages 303-306, Montreal, Canada, July/August 2002, has the disadvantage that the required tracking modes are not propagable in the reception path. Thus, it is not possible to acquire a correction signal. For this reason, the method described there is not suitable for a tracking application.